diff --git a/DeDRM_plugin/DeDRM_Kindle for Mac and PC Key_Help.htm b/DeDRM_plugin/DeDRM_Kindle for Mac and PC Key_Help.htm
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--- a/DeDRM_plugin/DeDRM_Kindle for Mac and PC Key_Help.htm	
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@@ -22,6 +22,8 @@ li {margin-top: 0.5em}
 
 <p>If you have upgraded from an earlier version of the plugin, any existing Kindle for Mac/PC keys will have been automatically imported, so you might not need to do any more configuration. In addition, on Windows and Mac, the default Kindle for Mac/PC key is added the first time the plugin is run. Continue reading for key generation and management instructions.</p>
 
+<p>Note that for best results, you should run Calibre / this plugin on the same machine where Kindle 4 PC / Kindle 4 Mac is running. It is possible to export/import the keys to another machine, but this may not always work, particularly with the newer DRM versions.</p>
+
 <h3>Creating New Keys:</h3>
 
 <p>On the right-hand side of the plugin’s customization dialog, you will see a button with an icon that looks like a green plus sign (+). Clicking this button will open a new dialog prompting you to enter a key name for the default Kindle for Mac/PC key. </p>